ABSTRACT PAYNE, JOSHUA BILL. Modeling the Growth and Death
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ABSTRACT PAYNE, JOSHUA BILL. Modeling the Growth and Death Kinetics of Salmonella in Poultry Litter as a Function of pH and Water Activity. (Under the direction of Dr. Brian W. Sheldon.) In order to assess Salmonella dynamics in a poultry production setting, two studies were conducted to evaluate how common environmental factors during production influence Salmonella populations in poultry litter. A field study was initially conducted to determine Salmonella prevalence, populations, serotypes, and antibiotic resistance in fresh excreta and litter from commercial North Carolina broiler farms. Litter pH, temperature, ammonia levels, moisture content, and water activity (Aw) were also measured. The purpose of this field study was to assess the populations and prevalence of Salmonella present during grow-out along with how varying environmental growth parameters and management practices impact its growth, persistence and true risk for consumers. Field data were subsequently used to design a laboratory study that observed the combined effects of pH and Aw at a constant temperature on the growth and decline of Salmonella spp. in inoculated litter for the purpose of predicting microbial behavior using statistical modeling. By understanding the growth and death kinetics of Salmonella based on environmental factors found normally during poultry production, production management strategies can be developed to reduce Salmonella populations on birds entering processing plants, thereby reducing the risk of foodborne illness for consumers. MODELING THE GROWTH AND DEATH KINETICS OF SALMONELLA IN POULTRY LITTER AS A FUNCTION OF pH AND WATER ACTIVITY By JOSHUA BILL PAYNE A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy ANIMAL SCIENCE AND POULTRY SCIENCE Raleigh 2005 APPROVED BY: _________________________ _________________________ Dr. Peter R. Ferket Dr. Jason A. Osborne _________________________ _________________________ Dr. Donna K. Carver Dr. Brian W. Sheldon Chair of Advisory Committee DEDICATION This dissertation is dedicated to my late father, Bill Payne, and my late sister, Lisa Gaston, who both passed away during my time spent pursuing a Ph.D. My father was an inspiration to me and those that knew him. As a proud son, I looked up to him as one of the most intelligent individuals that I have ever encountered. His constant, positive outlook on life amazed me and radiated from those that surrounded him. I will always cherish the time spent working cattle on our farm, riding horses, and fishing together and will keep those memories closest to my heart. It has truly been a blessing being raised by such a dear loving father and friend. Lisa was not only a sister but a best friend to me. Her charisma, friendliness, and outgoing personality appealed to many and is greatly missed. Both my father and my sister made a significant impact on the many lives that were fortunate enough to know two great and admired individuals. ii BIOGRAPHY Joshua Bill Payne, the son of Bill and Barbara Payne, was born on August 19, 1976 in Bull Shoals, Arkansas. He was raised on a farm in Gamaliel, Arkansas and graduated from Mountain Home High School in 1995. The author then enrolled at Arkansas State University, majored in Animal Science, and graduated cum laude with a Bachelor of Science degree in Agriculture in 1999. Upon graduation, Joshua was accepted into The Center of Excellence for Poultry Science at the University of Arkansas where he earned a Master of Science degree in Poultry Science under the direction of Dr. Susan E. Watkins in 2001. He then pursued a Doctor of Philosophy degree in Animal and Poultry Science at North Carolina State University (NCSU) under the supervision of Dr. Brian W. Sheldon. While at NCSU, Joshua met his future loving wife Sarah Ann Brown and the couple were married at Bald Head Island, North Carolina on May 8, 2004. iii ACKNOWLEDGEMENTS I am extremely grateful to my advisor, Dr. Brian Sheldon, for all his support and understanding throughout my Ph.D. experience. I consider it a privilege to learn from such a professional. I would also like to thank Dr. Jason Osborne, Dr. Donna Carver and Dr. Peter Ferket for their guidance as graduate committee members. Many hours were spent in Dr. Osborne’s office wading through pages of statistical output and I truly appreciate your time and effort. I am very thankful for the help of Pam Jenkins who spent countless hours helping me with statistics. I am indebted to Robert Neely for lending advice and assistance with my research. I would also like to acknowledge the entire Poultry Science Department Faculty, Staff and Graduate Students for their assistance, support and friendships. The financial support received from the North Carolina Agriculture Foundation is greatly appreciated as well. As always, I would like to especially thank my mother and late father for their unconditional love and support. Lastly, I would like to express my sincere gratitude and love to my wife Sarah. Your support, encouragement, love and devotion through both ideal and difficult circumstances have helped me to make it to this point. iv TABLE OF CONTENTS Page LIST OF TABLES ............................................................................................. viii LIST OF FIGURES ............................................................................................. ix INTRODUCTION..................................................................................................1 LITERATURE REVIEW .....................................................................................6 I. Salmonella Classification ................................................................................6 II. Salmonella Growth Parameters......................................................................8 A. Temperature ..............................................................................................8 B. Water Activity (Aw) ..................................................................................9 C. pH............................................................................................................12 III. Presence of Salmonella in Poultry Production............................................15 IV. Environmental Concerns ............................................................................17 V. Antibiotic Resistance ...................................................................................20 VI. Control Strategies .......................................................................................23 A. Disinfection.............................................................................................26 B. Litter Treatments.....................................................................................28 C. Best Management Practices ....................................................................30 1. House Construction.............................................................................30 2. Relative Humidity (RH) and Ventilation............................................31 v 3. Biosecurity ..........................................................................................34 4. Vaccines..............................................................................................36 5. Competitive Exclusion and Probiotics................................................37 6. Prebiotics.............................................................................................39 7. Bacteriophages....................................................................................41 VII. Observations of Salmonella Growth Behavior..........................................43 VIII. Predictive Modeling.................................................................................45 A. Gompertz Model .....................................................................................48 B. Baranyi Model.........................................................................................49 C. Log-Linear Model ...................................................................................50 D. Vitalistic Model.......................................................................................50 E. Churchill Model.......................................................................................51 F. Modeling Limitations ..............................................................................53 G. Modeling Applications for Poultry Production.......................................53 H. Objectives................................................................................................55 REFERENCES.....................................................................................................56 MANUSCRIPT 1 .................................................................................................71 Title Page: Characterization of Salmonella spp. prevalence, populations, serotypes, and antibiotic resistance in commercial broiler production.............72 Abstract.............................................................................................................73 Introduction.......................................................................................................74 Materials and Methods......................................................................................76 Results and Discussion .....................................................................................81